Radio relay control system



Apri14, 1944. J, SMWH 2,345,951

RADIO RELAY CONTROL SYSTEM Filed March 19, 1942 2 Sheets-Sheet 1 Tlz'j..

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April 4, 1944. J 'E SMITH i 2,345,951

RADIO RELAY CONTROL SYSTEM 'BY Mmw ATT'ORNEY -unattended andautomaticvin operation.

.sound channel. eration in either direction by merely reversing PatentedApr. 4, 1944 Ernest Smith, Brooklyn, N. Y., assigner to RadioCorporation of America, a corporation of Delaware Application March 19,1942, Serial No. 435,271

7 claims. lol. 25o-15) The present invention relates to radio'relaysystems and, more particularly, to organizations included in suchsystems for controlling and monitoring the operation of the componentstations of the system. Radio relay systems operating inthe neighborhoodof 500 megacyclesmust be composed of a great number of individualrepeater stations. In the present state of vthe art it is necessary forthese individual repeater or booster stations to be spaced about 15miles apart. It is desirable that most of these stations be To operatethis chain of relay stations satisfactorily,

-a control system must be incorporated by means of which the operationof the unattended stations may be initiated and concluded when desiredand by means of which the manner of operation may be supervised ormonitored from attended stationsin the system.

An object, therefore, of the present invention is the provision of aradio relay system utilizing a minimum amount of control equipment. v

Another object of the present invention is the provision of a method ofand a means for monitoring the operation of repeater stations in asystem, as aforesaid.

The foregoing objects, and others which may hereinafterappear, areattained by providing a relay system comprising a series of AattendedAmaster stations separated by unattended satellite repeater stations.

In one embodiment of the present invention, each satellite stationcontains a main transmitter and receiver operating to relay one type ofsignals such as the video portion of a television signal, an ancillarytransmitter and receiver operating to relay the associated sound portionof a rtelevision signal, as well as operating instructions and controlsystems. Each station also includes associated control and testequipment entirely operative from preceding and succeeding masterstations by code impulses, such as gnerated by telephone dial equipmenttransmitted over the sound channel. that two carrier frequencies bealternated throughout the video channel and two similarly alternatedcarrier frequencies in the ancillary This arrangement permits opthetransmitting and receiving antenna directivities without the necessityof returning the receivers and transmitters. It is assumed that the bandWidth of the video transmitting `and receiving antennas isV suicient toinclude each car- It is contemplatedk rier and its associated side bandswithout 4frequency discrimination. Each masterstation-oi the system isarranged to perform the following functions withv respect to each of itssatellite unattended repeaters: Y

1. Start and stop the transmitting and receiving equipment; i

2. Monitor the radio frequency output of each which is accompanied bydrawings in which Figure 1 illustrates a representative layout of arelay system employing master and satellite stations and the relation ofoperating Vfrequencies-which may be used; Figure 2 illustrates, inconventional block diagram formation, one typica] unattended station,while Figure 3 is a curve illustrating the operation of a portion ofFigure 2, and Figure 4 illustrates a modification of the embodiment ofFigure 2. Y

The relay system illustrated in Figure 1 consists of a master station Mwhich may, for example, be assumed to be atthe-west end of the relaysystem. Extending in an eastward direction therefrom are locatedsatellite repeater'stations A, B, C, D. The stations have their videochannels adjusted to operate on frequencies f1, fz, alternately.v Thusthe video receiver at A is required to receive signals of frequency f1from station M or station B and is also Vrequired to reject signals offrequency f1 from station D. Since station A is at a distance fromstation D three times that from station B, the signals from stationBwill be much weaker and Will be re jected due to the Well-knowndiscrimination of frequency modulation reception even thoughthe stationsare arranged in a straight line so that the characteristics of theantennae overlap. No diiculty attends the reception atstation A voffrequency f1 from station M without'interfer'- ence from stations B, D,etc., also operating on frequency f1 due to the employment ofdirectional antenna structures at each station. A repeater` stationtypical of any of the stations A, B, C, D of Figure l is shown in Figure2. The ancillary receiver I operates continuously so that any signalradiated at an immediately preceding station such as M and picked up byreceiving antenna WSA will be applied to selector switch I3 associatedwith receiver I0, assuming, of course, that at that time the switch 22is in the proper position. All of the other equipment at each satellitestation is energized from the power supply source only when relay II isenergized. If it is assumed that the relay system is to be placed intooperation and the operating characteristics checked, the operator at themaster station M dials, or otherwise transmits, a code combination whichactuates selector switch I3 to the proper position to energize relay IIthus starting the sound transmitter I5 and the video channel receiverand transmitter Il-IS. The advantages of operating an entire chain ofrelay stations on two alternating frequencies -f1 and f2 and structures-for enabling such operation is disclosed and described in detail in myapplication, Serial #430.527, filed February 12, 1942, to whichreference may be had if a more complete disclosure is desired. However,for the purposes of understanding the present invention, it is believedsufficient to merely assume that the relay stations are operated on twoalternating frequencies f1 and f2.

Once the sound transmitter is on the air, any further signallingimpulses picked up by antenna WSA will be transmitted from soundtransmitter I5 over the eastwardly directed antenna ESA, as indicated byarrow E at that antenna. Then the master station M, by transmittingfurther appropriate signal impulses, starts the succeeding satellitestations B, C, D in consecutive order. The master station M thennotifies the operator at station M1 over the sound channel that he isready for a test of the equipment. The operator at the master station Mthen again contacts repeater station at D and by means of a properselection of code signals sets switch 20 in position T and switch 22 inthe west-to-east transmission direction, as indicated by referencecharacter WE. Radio frequency excitation from video transmitter I9 thenfeeds antenna EVA and converter 24. The energy radiated from antenna EVAis received and utilized in receiver circuits at station M1. Theconverter 24 combines a radio frequency discriminator circuit andamplitude detector. Frequency modulation or frequency deviation from astandard frequency is thereby converted into amplitude variationsrepresentative of the frequency deviation. Thus with no modulatingsignal applied to video transmitter I9 and rigid limiting in its outputstage, a direct bias voltage is developed in converter 24 and applied tothe frequency shift oscillator 26. The magnitude of the voltage isdirectly proportional to the carrier frequency of video transmitter i9as shown by the curve 25 in Figure 3.

The frequency shift oscillator includes two radio frequency oscillatorsand a mixer in a conventional beat frequency oscillator circuit. Oneoscillator is tuned to a fixed radio frequency while the other has itsresonant circuit shunted by a variable reactance tube. Thus variationsin the modulator grid bias cause the beat note output of oscillator 26to vary in accordance with the variations in frequency of transmitterI9. When the video transmitter I9 is unmodulated, the bias voltage fromconverter' 24 produces a steady tone frequency modulation of the soundtransmitter I5. This is transmitted by wayv of antenna ESA to station M1where a chart ls available showing the relation between the radiofrequency with respect to the received tone frequency. Structure of theconverter 24 and the frequency shift oscillator 26 may, if desired, beof the type shown in Peterson Patent #2,291,558,

granted July 28, 1942, on application Serial No.V

365,584, filed November 14, 1940.

The operator at master station M then applies a test signal to the videotransmitter at that location. For example, this signal may be a 60 cyclesquare wave of some accurately known and predetermined amplitude. Theamplitude of the signal received out of the monitor receiver at stationM1 is direct indication of the power output of the video channel fromstation M through each of the relay stations A, B, C, D. ByV observingthe square wave signalling over the video channel on an oscilloscope,the operator at station M1 may determine that the video receiver isoperating normally. If the video signal is ab'- normal, each repeaterstation A, B, C, D must be separately tested to determine the locationof the trouble. In the special case, for example, where the trouble isin the video channel at station D this will be evident when the relaysystem, including the stations up to and including station C, has beenchecked and determined lto be properly operating, as hereinafterdescribed. After the system has been put into operation and theoperation of the video transmitter I9 at station C checked, asdescribed, the operator at station M notifies the operator at station M1that he is ready for a report. To receive this report, the operator atstation M sets switches 22 in the EW position at relay stations D, C, Band A in the order mentioned. The operator at the station M1 thenreverses his antenna switch manually and reports by sound channel to theoperator at the master station M. The operator at station M1 now hascontrol of all the intermediate repeaters. Hence,.after completing hisreport, he reverses the switches 22 at each of the satellite stations inthe order A, B, C, D. When this has been done, station M again hascontrol and can proceed to test repeater C by operating switch 20 toposition T and with the operator at station M1 monitoring the signalreceived over the sound channel. The direction of transmission isagain'reversed for the operator at station M1 to report to station M.After the report is made the channel is again changed to its originaldirection of transmission. This process is continued until all repeatersand the video transmitters therein have been checked. The chain is thendirected properly from west to east and all master stations may awaitfurther orders Joy way of the sound channel.

It should be noted that the antenna switch 22 has been shown by way ofillustration as a relay operated tandem of two double pole, double-throwswitches. In practice, if such switches are used, they should be of suchtype that their impedance is not greatly diierent from the impedance ofthe transmission lines into which they are connected to prevent theintroduction of reflections and loss of power. If desired, the antennaswitches may be replaced by a physically rotatable antenna arrangement.Furthermore, the directivity of the antennae may be reversed by properlyphasing the connections of the antenna and feed lines connected'thereto,as taught by N. E. Lindenblad in his prior agonisti 1940, and

'from that shown in Figure 2 in that'at each station, one sound channel,including receiving antenna WRA, receiver l0, transmitter l5, andtransmitting antenna ETA, is provided for transmitting in a west-to-eastdirection. A second sound channel operating in an east-to-west'directionis provided including an eastwardly directed receiving antenna ERA,receiver 311, a transmitter 35, and a westwardly directed antenna WTA.This arrangement, providing a twoway sound channel, permitsinstantaneous and continuous communication between a pair of adjacentmaster stations Without the necessity cf reversing the direction oftransmission of the video channel of each of the satellite stations A,B, C, D. The direction of transmission of the video channel is, asbefore, reversed by switch 22 operating under control of selector switchI3 actuated in respo-nse to control impulses over the sound channels,The operation of switch 20 for monito-ring the frequency of operation ofvideo transmitter I9 is as heretofore described, except that themonitoring tone is reverted to the preceding master station instead ofbeing forwarded to the following station. Thus the time lost in makingindividual reports from station M1 to station M for each interveningstation A, B, C, D is avoided. As a matter of fact, the presence of anoperator at station M is not necessary during the preliminary testingperiod.

While I have shown and particularly described several embodiments of myinvention, it is to be distinctly understood that my invention is notlimited thereto but that modifications Within the scope of my inventionmay be made.

I claim:

1. The method of monitoring the operation of an unattended relay stationwhich comprises generating at said station, in response to controlsignals from a preceding master station, an audiov frequency oscillationhaving a frequency proportional to the frequency of operation of atransmitter at said relay station, receiving said oscillation at asucceeding master station and measuring the frequency of saidoscillations.

2. The method of monitoring the operation of an unattended relay stationwhich comprises generating at said station, in response to controlsignals from a preceding master station, an audio frequency oscillationhaving a frequency proportional to the frequency of operation of atransmitter at said relay station, receiving said oscillation at asucceeding master station, and measuring the frequency of saidoscillations, frequency modulating said transmitter in response tosquare wave signals from said preceding master station, receiving atsaid succeeding master station the square wave frequency modulated wavefrom said transmitter, demodulating said received wave, and comparingsaid demodulated received Wave with said received oscillations.

3. A relay system including a plurality of master stations and at leastone unattended satellite station therebetween, each station includingmain transmitting and receiving equipment operative on one frequency andnormally so arranged as to receive signals from one adjacent station andtransmit signals to another adjacent station, Vancillary transmittingand receiving equipment operative on another frequency, the ancillaryreceiving equipment at each of said satellite stations beingcontinuously energized,

means 'responsive to control signals received by said ancillaryreceiving equipment for energizing the remaining equipment at saidstation, means responsive to further control signals for reversing thedirection of transmission of signals, means at said satellite stationsfor generating 'an audio frequency 'oscillation having its frequencydependent upon the frequency of operation of the main transmittingequipment at said station and means responsive to control signals forapplying said audio frequency oscillations to said ancillarytransmitting equipment.

f4. A relay system including a plurality o master stations and at leastone unattended lsatellite station therebetween, each station inmentoperative on one frequency, ancillary transmitting and receivingequipment operative on another frequency, said equipment being normallyso arranged as to receive signals from one adjacent station and transmitsignals to another adjacent station, the ancillary receiving equipmentat each of said satellite stations being continuously energized, meansresponsive to control signals received by said ancillary receivingequipment for energizing the remaining equipment at said station, meansresponsive to further control signals for reversing the direction oftransmission of signals, means at Said satellite stations for generatingan audio frequency oscillation having its frequency dependent Aupon thefrequency oi operation of the main transmitting equipment at saidstation, and means responsive to control signals for applying said audiofrequency osci1 lations to said ancillary transmitting equipments.

5. A relay system including a plurality of master stations and at leastone unattended satellite station therebetween, each station includingmain transmitting and receiving equipment operative on one frequency andso arranged as to receive signals from one adjacent station and transmitsignals to another adjacent station, ancillary transmitting andreceiving equipment operative on another frequency, and similarly arranged for transmission and reception, the ancillary receiving equipmentat each of said satellite stations being continuously energized, meansresponsive to co-ntrcl signals received by said ancillary receivingequipment for energizing the remaining equipment at said station, meansat said satellite stations for generating an audio frequency oscillationhaving its frequency dependent upon the frequency of operation of themain transmitting equipment at Said station, and means responsive tocontrol signals for applying said audio frequency oscillations to saidancillary transmitting equipment.

6. A relay system including a plurality of master stations and at leastone unattended satellite station therebetween, each station includingmain transmitting and receiving equipment operative on one frequency,normally so arranged as to receive signals from one adjacent station andtransmit signals to another adjacent station, rst and second ancillarytransmitting and receiving equipment operative on another frequency,each of said ancillary receivers and transmitters being arranged toreceive and transmit signals to one of said adjacent stations, theancillary receiving equipment at each of said satellite stations beingcontinuously energized, means responsive to control signals received bysaid ancillary receiving equipment for energizing the remainingequipment at said station, means at said satellite stations forgenerating an audio frequency oscillation having its frequency dependentupon the frequency of operation of the main transmitting equipment atsaid station, and means responsive to control signals for applying saidaudio frequency oscillations to said ancillary transmitting equipment.

7. A satellite radio relay station adapted for use in a relay systemincluding a plurality of master stations and at least one unattendedsatellite station therebetween, said satellite station including maintransmitting and receiving equipment operative on one frequency,normally so arranged as to receive signals from an adjacent station andtransmit signals to another adjacent station, rst and second ancillarytransmitting and receiving equipment operative on another frequency,each of said ancillary receivers and 'transmitters Vbeing arranged toreceive and .transmit signals to one of said adjacent stations, theancillary receiving equipment at said satellite station beingcontinuously energized, means responsive to control signals received bysaid ancillary receiving equipment for energizing the remainingequipment at said satellite station, means at said satellitestation for'generating an audio frequency oscillation having its frequency dependentupon the frequency of operation of the main transmitting equipment atsaid station, and means responsive to control signals for applying saidaudio frequency oscillations to said ancillary transmitting equipment.

J. ERNEST SMITH.

